Offshore natural gas, comprising methane and higher hydrocarbons such as ethane, propane and butane, is often recovered directly, or as an associated gas with oil production, using fixed or floating platforms coupled to well heads on the seabed. The recovered natural gas is, where generally possible, fed via pipeline to on-shore gas processing facilities where such steps as purification may be carried out. However for a significant proportion of the recovered natural gas, pipelining to on-shore facilities is not possible. In such cases it has become desirable to recover and liquefy the natural gas for sea transportation to on-shore facilities. The liquefaction processes typically include steps of cooling the natural gas to a very low temperature, which allows separation of at least some of the ethane, propane, butanes and other higher hydrocarbons from the methane. The liquefied products have different commercial values, but offshore where further processing such as cracking is not feasible, typically the ethane has the lowest value and so part is often used for power generation in the liquefaction facility and the excess is flared. Alternatively, the excess ethane may be recovered and transported with the LNG to the onshore facility. However the economics of transporting ethane in place of the more valuable liquids is less attractive. With ever-increasing pressure on maximising the utilisation of the recovered hydrocarbons coupled with a need to reduce flaring, which has become environmentally unsound, there is a need for an improved process for treating offshore natural gas.
The CRG (Catalytic Rich Gas) process, developed originally by British Gas and licensed by Davy Process Technology Ltd, utilises a combination of steam reforming, methanation and CO2 removal to generate synthetic natural gases from LPG (liquefied petroleum gas) or naphtha. Alternatively, CRG steam reforming has been used as a means to lower the calorific value of LNG-derived natural gas destined for pipeline supplies.